1. Field of the Invention
This invention relates to a so-called shutter-type clamping device.
2. Description of the Related Art
FIGS. 5 and 6 shows a conventional shutter-type clamping device for use in an injection molding machine or the like (U.S. Pat. No. 4,201,553).
The device shown includes a stationary platen 2, a movable platen 4, a base plate 6, tie bars 8A through 8D, and molds 10A and 10B respectively attached to the stationary and movable platens 2 and 4.
Provided on the base plate 6 is a clamping piston 12 having a hollow section 12A. The reference numeral 14 indicates a cylinder firmly attached to the base plate 6, and, the reference numeral 16 indicates a flange provided at the opening of the cylinder 14.
Provided on the movable platen 4 is a protrusion 18, which is composed of a nut 18A and a screw bolt 18B. This protrusion 18 has the function of adjusting the mold thickness by varying the length of that section thereof in which the nut and the screw bolt are engaged with each other, and is formed as a cylinder whose size is such that it can enter the hollow section 12A of the piston 12 mentioned above.
Provided between the piston 12 and the protrusion 18 is a shutter 20, by means of which the end opening of the hollow section 12A can be closed. This shutter 20 is arranged in such a manner as to be slidable along the tie bar 8A and as to be able to appropriately follow the axial movement of the piston 12 by means of a shutter gap adjustment mechanism 22.
As shown in FIG. 6, this shutter 20 consists of a swing arm 20B adapted to swing around the tie bar 8A, and a shutter body 20A attached to this swing arm, with the hollow section 12A of the piston 12 being opened and closed by a cylinder 28.
The reference numeral 26 indicates a moving cylinder for opening and closing the movable platen 4.
This conventional shutter-type clamping device, constructed as described above, closes the shutter 20 when performing clamping, transmitting the pressing force of the clamping piston 12 to the movable platen 4 through the protrusion 18. When opening or closing the movable platen 4, the shutter 20 is opened, whereby the protrusion 18 of the movable plate 4 is allowed to enter the hollow section 12A of the piston 12, so that the movable platen 4 can retreat.
In this conventional shutter-type clamping device, however, the shutter 20, or the cylinder 28 for driving the same, is attached to the tie bar 8A or 8D, so that the shutter 20, the cylinder 28, which drives it, and the piston 12 make separate movements, resulting in an unstable shutter operation, which has a bad influence on the mounting quality of the members connecting the shutter 20 and the shutter driving cylinder 28 with each other.
In this conventional example, shown in FIGS. 5 and 6, the above-mentioned trouble is mitigated to some degree by the provision of the shutter gap adjustment mechanism 22, which, however, is liable to make the device construction rather complicated, resulting in a low level of operational efficiency in the assembly and replacement of the members related to the shutter and, consequently, in high costs. Further, despite the presence of this shutter gap adjustment mechanism 22, etc., it has been difficult to maintain a sufficiently high level of operational safety with respect to the shutter opening/closing operation.